<template>
  <div :class="[prefixCls + '-alpha']" tabindex="0" @click="$el.focus()" @keydown.esc="handleEscape" @keydown.left="handleLeft" @keydown.right="handleRight" @keydown.up="handleUp" @keydown.down="handleDown">
    <div :class="[prefixCls + '-alpha-checkboard-wrap']">
      <div :class="[prefixCls + '-alpha-checkerboard']"></div>
    </div>
    <div :style="gradientStyle" :class="[prefixCls + '-alpha-gradient']"></div>
    <div ref="container" :class="[prefixCls + '-alpha-container']" @mousedown="handleMouseDown" @touchmove="handleChange" @touchstart="handleChange">
      <div :style="{top: 0, left: `${value.a * 100}%`}" :class="[prefixCls + '-alpha-pointer']">
        <div :class="[prefixCls + '-alpha-picker']"></div>
      </div>
    </div>
  </div>
</template>

<script>
import HSAMixin from './hsaMixin';
import Prefixes from './prefixMixin';
import { clamp, toRGBAString } from './utils';

export default {
  name: 'Alpha',

  mixins: [HSAMixin, Prefixes],

  data() {
    const normalStep = 1;
    const jumpStep = 10;

    return {
      left: -normalStep,
      right: normalStep,
      up: jumpStep,
      down: -jumpStep,
      powerKey: 'shiftKey'
    };
  },

  computed: {
    gradientStyle() {
      const { r, g, b } = this.value.rgba;
      const start = toRGBAString({ r, g, b, a: 0 });
      const finish = toRGBAString({ r, g, b, a: 1 });

      return { background: `linear-gradient(to right, ${start} 0%, ${finish} 100%)` };
    }
  },

  methods: {
    change(newAlpha) {
      const { h, s, l } = this.value.hsl;
      const { a } = this.value;

      if (a !== newAlpha) {
        this.$emit('change', { h, s, l, a: newAlpha, source: 'rgba' });
      }
    },
    handleSlide(e, direction) {
      e.preventDefault();
      e.stopPropagation();

      this.change(clamp(e[this.powerKey] ? direction : Math.round(this.value.hsl.a * 100 + direction) / 100, 0, 1));
    },
    handleChange(e) {
      e.preventDefault();
      e.stopPropagation();

      const left = this.getLeft(e);

      if (left < 0) {
        this.change(0);
        return;
      }

      const { clientWidth } = this.$refs.container;

      if (left > clientWidth) {
        this.change(1);
        return;
      }

      this.change(Math.round((left * 100) / clientWidth) / 100);
    }
  }
};
</script>
